This invention relates to a device for braking a component in a change speed gearbox to facilitate shifting of the gearbox and, more particularly, to such a device having particular utility in the gearbox of an agricultural harvesting machine, such as a combine or the like.
The gearbox on an agricultural combine typically is shiftable into different ratios to provide different ground speed ranges for the combine. Such a machine is normally provided with a propulsion drive clutch, and the combine is normally stopped with the clutch disengaged when the gearbox is shifted into its alternate driving conditions. The gearbox shifting is typically accomplished by a simple shiftable collar that engages alternate gears, and when the combine is stopped and the clutch has been disengaged for a significant period, the shifting is accomplished without difficulty. However, the combine during operation in the field, is also normally stopped at relatively frequent intervals, during which the gearbox is placed in a neutral condition and the clutch is re-engaged, so that the transmission input shaft is driven, although the combine is standing still. Instances of this nature occur when the combine is stopped temporarily to allow a slug of crop material to clear the machine or when the grain tank of the combine is being unloaded. Since the input shaft of the gearbox is being driven, the gearbox components up to the shift collar, which is in its neutral position, will be driven, while the gearbox components downstream of the shift collar will be stopped, since they are connected to the stopped drive wheels. When the clutch is disengaged to disconnect the power source from the gearbox input shaft, the momentum of the rotating parts will cause the parts to continue rotating for a period of time, and if the operator tries to shift the collar into an engaged position, the shifting will be difficult since it will involve engagement of a stationary part with a rotating part.
Accordingly, it is known to provide a hydraulic brake that applies a braking force to the rotating gearbox parts simultaneously with the operation of the main clutch, such as shown in West German patent DE 2,913,859, which is also assigned to the assignee herein. However, in the braking arrangement shown in said patent, the hydraulically actuated brake is applied at the same time that the clutch pedal is depressed, so that the brake is applied whenever the clutch pedal is depressed. This means that the brake is applied on many occasions when it is not required.